LOGICAL DATABASE:
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To read data from a database tables we use logical database.
A logical database provides read-only access to a group of
related tables to an ABAP/4 program.

Advantages: i)check functions which check that user input is
complete, correct,and plausible. ii)Meaningful data
selection. iii)central authorization checks for database
accesses. iv)good read access performance while retaining
the hierarchical data view determined by the application
logic. dis advantages: i)If you donot specify a logical
database in the program attributes,the GET events never
occur. ii)There is no ENDGET command,so the code block
associated with an event ends with the next event statement
(such as another GET or an END-OF-SELECTION). 


Logical databases are special ABAP programs that retrieve
data and make it available to application programs. The most
common use of logical databases is still to read data from
database tables by linking them to executable ABAP programs.

          Logical databases contain Open SQL statements that
read data from the database. You do not therefore need to
use SQL in your own programs. The logical database reads the
program, stores them in the program if necessary, and then
passes them line by line to the application program or the
function module LDB_PROCESS using an interface work area.

         A logical database provides a particular view of
database tables in the R/3 System. It is always worth using
logical databases if the structure of the data that you want
to read corresponds to a view available through a logical
database.

       The data structure in a logical database is
hierarchical. Many tables in the R/3 System are linked to
each other using foreign key relationships. Some of these
dependencies form tree-like hierarchical structures. Logical
databases read data from database tables that are part of
these structures. 

Physical Database is actual Database.